As various electronic devices including a personal computer, a digital camera, and a mobile phone progress toward downsizing and higher performance, requirements are rapidly increasing for further downsizing, thinning, and higher density in a semiconductor device. Accordingly, it is desired to develop a photosensitive insulating material that can accommodate not only an increase in surface area of a substrate for the sake of higher productivity, but also a structure having fine concavity and convexity with high aspect ratio on a substrate, in high density mounting technologies including a chip size package or a chip scale package (CSP) and a three-dimensional lamination.
As the photosensitive insulating material, there has been proposed a photo-curable resin composition that can be applied with a wide range of film thickness by a spin coating method, which is commonly used in the semiconductor device fabrication, be processed into a fine pattern with a wide range of wavelength, and be post-cured at low temperature into a top coat having excellent flexibility, heat resistance, electric characteristics, adhesiveness, reliability, and chemical resistance to protect electric and electronic parts (PATENT LITERATURE 1). The spin coating method has an advantage of easily forming a film on a substrate.
The photo-curable resin composition for forming a top coat to protect electric and electronic parts is used with a film thickness of 1 to 100 μm on a substrate. Unfortunately, the photo-curable resin composition has a practical limit of forming a film by the spin coating method due to an increase in viscosity when film thickness exceeds about 30 μm.
Additionally, when the photo-curable resin composition is applied onto a substrate having an uneven surface by the spin coating method, the composition is difficult to coat the substrate uniformly. This easily causes the photo-curable resin layer to have voids on an uneven portion of the substrate. It would therefore be desirable to improve planarity and step coverage. As the alternative coating method of the spin coating method, a spray coating method has been proposed (PATENT LITERATURE 2). However, in principle, this method easily causes defects such as height difference due to unevenness of the substrate, film loss at pattern edge, and a pinhole in a recess bottom. Thus, the problems of planarity and step coverage still remain unsolved.
The recent high density mounting technologies including a chip size package or a chip scale package (CSP) and a three-dimensional lamination have strongly desired a material that allows forming a pattern of an ultrathick film exceeding 100 μm on a substrate and covering the pattern with metal such as copper for redistribution from a chip. To obtain a fine pattern, lithography is commonly used. Above all, a chemically amplified negative resist material is suitable to obtain a fine pattern. The pattern used for redistribution exists between device chips permanently and is required to function as a top coat that is curable and excellent in flexibility, heat resistance, electric characteristics, adhesiveness, reliability, and chemical resistance to protect electric and electronic parts. Thus, the resist composition for providing the pattern is preferably of a negative type.